1. Field of the Invention
The present invention relates to a polyurethane foam injected with strand mats, and more particularly to a method and an apparatus for manufacturing a polyurethane foam injected with strand mats, in which the upper surface of the polyurethane foam is made uniform and the physical properties such as the tensile strength, compression strength and the like of the polyurethane foam are equalized, resulting from maximally removing air spaces in the strand mats when the strand mats are immersed in a polyurethane foam solution.
2. Description of the Related Art
Generally, polyurethane foam is a porous material in the form of sponge, produced by a chemical reaction of a polyol and an isocyanate, along with other additives. It is divided into a flexible polyurethane foam and a rigid polyurethane foam. The flexible polyurethane foam is used primarily as a cushioning material such as a matrix and the rigid polyurethane foam is utilized mainly as an insulating material. The present invention focuses on the rigid polyurethane foam used for an insulating material, and in particular, a method and an apparatus for manufacturing a polyurethane foam reinforced with glass fibers, used as a cold-insulating material for a ship intended for transporting mainly a super-low temperature substance such as liquefied natural gas (LNG).
As shown in FIG. 1, a conventional manufacturing method of a polyurethane foam injected with strand mats comprises the steps of: continuously supplying and transferring the strand mats made with glass fiber, spraying a polyurethane foam solution on the strand mats so as to immerse the strand mats in the polyurethane foam solution, foam molding the polyurethane foam solution into a polyurethane foam after a designated time, and taking out the completed polyurethane foam from the manufacturing apparatus.
The strand mat is produced by binding glass fibers of less than 25 microns with a polyester binder to maintain the shape of the mat. In this case, the amount of the polyester binder must be minimized within an extent that the shape of the mat is maintained. Generally, the polyester binder is used in the range of 1.3 to 3 weight % of the strand mat.
Strand mat is supplied in a manner such that multiple strand mats are laminated, and then a polyurethane foam solution is sprayed on the laminated strand mats. When the strand mats are immersed in the polyurethane foam solution, a large number of air spaces are present in the strand mats. Generally, the air in the strand mats is exhausted outside the strand mats while the strand mats are immersed in the polyurethane foam solution. Then, the space that the air has been exhausted is filled with the polyurethane foam solution.
At a designated time after the strand mats are immersed in the polyurethane foam solution, the polyurethane foam solution is foam molded. However, air that is not exhausted to the outside in time, remains in a produced polyurethane foam, resulting in adversely influencing on insulation property of the polyurethane foam. Furthermore, the surface of the molded polyurethane foam is not uniform and a variety of the physical properties of the polyurethane foam are not uniform. As a result, the quality of the polyurethane foam is deteriorated.
More specifically, in the conventional method for manufacturing a polyurethane foam injected with strand mats, after the polyurethane foam solution is sprayed on the strand mats, it is foamed in a state wherein the air between glass fibers in the strand mats is not completely exhausted to the outside. As a result, a large number of air spaces are present in the molded polyurethane foam, resulting in the strength and cold-insulating effect of the polyurethane foam being reduced. Therefore, shrinkage, cracking and distortion and the like are caused in the polyurethane foam under a super-low temperature condition, or the polyurethane foam is liable to be broken by an external impact.